Electromagnetic device with reversible generator-motor operation

ABSTRACT

An electromagnetic device has a stator and a rotor rotating between facing surfaces of the stator and bearing a plurality of magnets distributed at regular intervals along its periphery. The magnets are so arranged that they form a sequence of alternately opposite poles on the surfaces of the rotor directed towards the stator, and the stator comprises two sets of independently supported magnetic yokes located at both sides of the rotor in front of the magnets. The magnetic yokes have two axially oriented arms, the end surfaces of which, in static conditions of the rotor, at least partly face a pair of successive magnets on a same surface of the rotor.

The present invention relates to an electromagnetic device withreversible generator-motor operation, that is, a device capable ofconverting kinetic energy into electric energy and vice versa.

In many industrial fields the need often arises to install reversibleelectrical machines into systems comprising a rotary member, so that,depending on the operating condition of the system in which a machine isinstalled, it is possible either exploiting the motion of such member togenerate electric energy for supplying other system components, orsupplying the machine with electric energy to make the rotary memberrotate.

A general requirement for such machines is compactness and lightness,especially for applications in transport means, such as terrestrialvehicles or aircrafts, as well as cheapness.

An example of a machine of this kind is known from U.S. Pat. No.6,832,486. This document discloses a reversible electrical machine foraeronautical applications, to be coupled with a turbine of an aircraftengine in order to generate electric energy for various purposes byexploiting the turbine rotation or, conversely, to start the engine. Therotor of the machine is formed by a magnetised, radially outwardextremity of the blades of a blade ring in the turbine. A stator ring,internally of which the rotor moves, is equipped with coils. In oneembodiment, the stator consists of a continuous ring, or of a set ofdiscrete horseshoe-shaped members, and defines a channel within whichthe rotor rotates. In this case, the coils are wound on opposite statorexpansions and they face both poles of a same magnet.

A drawback of this prior art is that the width of the channel definedbetween the facing expansions of the stator ring or of the individualhorseshoe-shaped cores is fixed and cannot become smaller than a certainminimum value, which depends also on the rotor thickness and on the needto compensate for possible rotor oscillations. Thus, with a given statorand a given rotor, also the air-gap between the stator and the magnetsis fixed and cannot be made smaller than a certain value. Consequently,it is impossible to adjust and optimise the relative position of thestator and the rotor so as to obtain the maximum efficiency and themaximum operating flexibility.

U.S. Pat. No. 5,514,923 discloses a reversible electrical machine thatcan be used as a flywheel, and that has two rotor discs equipped withmagnets and symmetrically arranged relative to a stator bearing aplurality of coils offset relative to the magnets. In such case, twomagnets are used to induce an electric field into a coil locatedtherebetween. The magnetic circuit is not closed and this entails a highenergy waste and results in strong electromagnetic interferences.

BE 867.436 discloses an electrical device having a rotor comprising twoaluminium discs joined by an iron ring and bearing each a plurality ofmagnets distributed at regular intervals along its periphery. The rotorrotates between two stator plates each bearing a ring of U-shapedmagnetic yokes with axially directed arms (projecting pole machine),wherein each yoke faces a pair of magnets in the rotor disc, and themagnets present, towards the yokes, a sequence of alternately oppositepoles. The machine is not reversible and acts only as a synchronousmotor. Moreover the air gap between the stator and the rotor is fixed,so that the considerations made in this respect in connection with U.S.Pat. No. 6,832,486 apply also to this device. Further, the materialsused give rise to very high losses at high frequencies and to verystrong Foucault currents and hysteresis losses that induce very hightemperatures in the disc and can lead to demagnetisation of the magnetsand even to the firing of the aluminium disc.

U.S. Pat. No. 6,137,203 discloses a brushless axial motor with twostators and a rotor rotatably mounted between the stators in response tomagnetic fields generated by the stators. The machine is a multiphasemachine of the “winding” type, i.e. the coils of each phase are woundover a plurality of adjacent polar expansions, without any coil ofdifferent phase between them. The stators are axially adjustable duringoperation to vary the motor's air gap in order to allow the motor toproduce a high torque at low speed, while the air gap is small, and tocontinue producing torque, when the air gap is larger, at high speed.Adjustment of the stator takes place only in axial direction and it doesnot allow coping with deformations arising because of the hightemperatures reached during the operation of the device, especially inthe preferred applications to fluid-operated turbines, nor with apossible overheating of the coils and the stator.

U.S. Pat. No. 4,710,667 discloses a dynamoelectric machine of thewinding type, in which the gap between the rotor and a stator isadjustable only axially and only in the assembling phase. The rotorincludes hard-ferrite magnets, and the stator includes soft-ferritecores for the coils.

All prior art documents discussed above disclose moreover rigidly builtstructures, whose design cannot be easily modified in order to suit toapplications with different requirements and/or to allow an easier andmore effective assembling and maintenance of the devices.

It is an object of the invention to provide a reversible device of theprojecting pole type, which remedies the drawbacks of the prior art andwhich can be employed in a wide range of applications, e.g. interrestrial vehicles, ships and aircrafts, and preferably inapplications in which the device is integrated in a turbine or generallyin the impeller of an apparatus driven by the motion of a fluid.

To attain this object, there is provided a device having a stator and arotor rotating in front of the stator. The rotor bears a plurality ofmagnets distributed at regular intervals and with alternate orientationsin a ring pattern on the rotor. The stator comprises at least one set ofmagnetic yokes each having a pair of projecting arms extending towardsthe rotor and bearing a coil for electrical connection to a utilisingdevice or a power driver, and a magnetic yoke in the or each set ispart, together with a pair of magnets confronting the yoke arms at agiven instant and the air gap separating the yoke from the magnets, of asame closed magnetic circuit. The magnetic yokes in the or each set areindependently mounted on axially and radially adjustable supports for astatic and dynamic adjustment of the positions of the yokes relative tothe magnets.

Advantageously, adjustment can include also a pivotal movement about atleast one axis and preferably the yokes are adjustable through atranslational movement along three orthogonal axes and a pivotalmovement about three orthogonal axes.

Thanks to the independent mounting, each yoke can be considered as astator cell that can be replicated a desired number of times and withany desired relative position with the other cells. Thus, the inventionaffords an extremely high flexibility. Other advantages are that:

-   -   assembling of the device is easier;    -   the relative position of yokes and magnets can be optimised when        assembling the device, thereby ensuring the maximum efficiency        of the device;    -   during operation, oscillations, vibrations and deformations of        the rotor can be easily compensated for;    -   in case of bad operation or short-circuits in one cell, it is        possible to exclude from operation only that cell, while the        rest of the device continues operating;    -   in case of a modular machine having both generator and motor        modules, it is possible to adjust independently the performance        of the generator and motor modules: e.g., at the start, the        distance of the yokes of the generator modules can be increased        to temporarily disable or set to a limited value the generator        function or yet to electronically leave the utilising circuits        open in order to facilitate starting, whereas the yokes of the        motor modules can be brought closer to the magnets in order to        increase acceleration.

A single set of yokes can be provided, and the magnets then form thesequence of alternate poles on one surface of the rotor. The rotor maybe made of ferromagnetic material, in which case the magnetic circuitscomprise a pair of magnets and one yoke and are closed through the airgap and the rotor. If, in the areas not occupied by the magnets, therotor is made of non-ferromagnetic material, the magnets facing a sameyoke will be connected by ferromagnetic elements, and the magneticcircuit is closed through the air gap and said ferromagnetic element.

In the alternative, when the rotor, in the areas not occupied by themagnets, is made of non-ferromagnetic material, the stator can includetwo sets of magnetic yokes symmetrically arranged relative to the rotor.In such case, a pair of successive magnets forms a closed magneticcircuit with one magnetic yoke in the first set and one magnetic yoke inthe second set (plus, of course, the respective air gaps). The yokes ineach set are supported independently of the yokes in the other set.

The or each set of yokes can face the whole ring of magnets, or it canface only one arc or discrete arcs of such ring.

When the yokes face the whole ring of magnets, the rotor can bear anumber of magnets twice the number of yokes (that is a number of magnetsequal to the number of projecting arms or polar expansions), or it canbear an even number of magnets different from the number of polarexpansions. In the latter case, a given geometrical phase relationshipbetween an arm and confronting magnet periodically occurs. Thoseconfigurations are suitable for building multiphase machines. In suchconfigurations, coils for collection or supply of electric power woundon arms having the same geometrical phase relationship with aconfronting magnet can be connected together inside the device and havea common connection to the power driver or the utilising device. It isalso possible to connect together every second coil among the coilswound on arms having the same geometrical phase relationship with aconfronting magnet, and to connect the two resulting coil groups to thepower driver or the utilising device with electrical phases shifted by180°.

The device can find several applications, especially in association withan impeller of an apparatus driven by the motion of a fluid, inparticular in Aeolian generators or in aeronautical or naval turbineengines or propellers: for instance, in aeronautical or navalapplications it can be used for instance as a generator integrated intothe turbine or as a starting or feedback motor for the turbine, or amotor associated with naval or aeronautical propellers. Otherapplications can be in pumps for gas pipelines.

According to another aspect, the invention also concerns the impeller ofan apparatus driven by the motion of a fluid, e.g. an Aeolian generator,a turbine engine for aircrafts or ships, a screw of naval andaeronautical propellers, a pump for gas pipelines and the like, havingintegrated therein a device according to the invention.

The device according to the invention will now be described in greaterdetail with reference to the accompanying drawings, given by way of nonlimiting examples, in which:

FIG. 1 is a perspective view of a first embodiment of the deviceaccording to the invention, with axial mounting;

FIG. 2 is a perspective view of the rotor of the device shown in FIG. 1,with a pair of yokes and the associated coils;

FIG. 3 is a schematic representation of a magnetic circuit;

FIG. 4 is a schematic representation of the spatial relationship betweenmagnets and yokes during rotation of the rotor;

FIGS. 5 and 6 are views similar to FIGS. 2 and 3, relating to a variantof the axial-mounting embodiment;

FIG. 7 is a schematic view of a variant of the embodiment of FIGS. 1 to3, with yokes located in front of discrete sectors only of the magnetring;

FIGS. 8 to 12 are schematic views of a number of embodiments with radialmounting of the magnets and the yokes;

FIGS. 13 to 15 are schematic views showing a number of magnet and yokepatterns used in multiphase machines;

FIGS. 16 and 16 b are enlarged axial section of a yoke arm and of ayoke, respectively, as used in the multiphase machines of FIGS. 13 to15;

FIGS. 17( a) to 17(d) are different views of a magnet with a doubletapering;

FIGS. 18 and 19 are plan views of part of a radial machine with externaland internal rotor, respectively, showing possible mountings of themagnets;

FIGS. 20 to 22 are different views of a yoke associated with means foradjusting its position;

FIG. 23 shows a yoke embodied in a resin layer;

FIG. 24 shows a yoke together with the indications of the translationaland pivotal adjustments;

FIG. 25 is a chart of the magnetic permeability of a ferrite;

FIG. 26 shows the application of the invention to a ship or aircraftpropeller;

FIG. 27 is a principle diagram of a stator cell; and

FIG. 28 is a principle diagram showing the use of the device as anelectromagnetic flywheel.

Referring to FIGS. 1 to 3, there is shown a first embodiment of thedevice according to the invention, generally indicated by referencenumeral 10, intended to build an axial machine.

Device 10 mainly comprises two distinct structures.

The first structure is a disc or a ring 12 (for sake of simplicity,herein below reference will be made to a disc), which forms the rotor ofdevice 10 and is mounted on a shaft 13. The main surfaces of disc 12bear a ring of identical permanent magnets 14 distributed in regularmanner along its circumference, near the outer disc edge. Magnets 14 arearranged so as to form, on each surface of disc 12, a succession ofalternately opposite poles. In the embodiment shown in FIGS. 1 to 3,disc 12, in the areas not occupied by magnets 14, is made ofnon-ferromagnetic material.

The central portion of disc 12 is formed with a plurality of blades 15having propulsive function and conveying cooling air towards magnets 14as well as towards coils, discussed below, for collection/supply ofelectric power generated by the device or intended for it.

Magnets 14 may have circular cross section, as shown in FIG. 2, or adifferent curvilinear cross-section, or yet a polygonal cross section,either convex (in particular square or rectangular) or concave.

Advantageously, the magnets are made of a material with high fieldintensity (e.g. about 1.5 Tesla with today's technology). The choice ofthe material will depend on the kind of application and hence on theoperating conditions, in particular on the temperature of the operatingenvironment. Materials commonly used in such machines are NdFeB,enabling operation at temperatures up to 150° C., or Sm—Co (or generallyrare earth-cobalt), enabling operation at temperatures up to 350° C., orAlNiCo, enabling operation at temperatures up to 500° C. Depending onthe materials, magnets 14 can consist of magnetised areas of disc 12, orthey can be magnetic bodies inserted into seats formed in the disc.

The second structure consists of two sets of magnetic yokes 16, 18 thatare arranged in a respective ring around disc 12, symmetrically thereto,and form the stator of the device. In the illustrated example, magneticyokes 16, 18 are distributed in regular manner around disc 12, in frontof magnets 14. The yokes have substantially a C or U shape, or generallya concave shape, open towards disc 12, with two substantially parallelarms or polar expansions denoted 17 a, 17 b for yokes 16 and 19 a, 19 bfor yokes 18 (see FIG. 3). Arms 17 a, 17 b and 19 a, 19 b bear coils 20a, 20 b and 22 a, 22 b, respectively, of electrically conductivematerial (e.g. copper or aluminium, the latter being preferred inaeronautical applications due to its lower specific weight), withrespective individual connections either to utilisation devices of thegenerated electric power or to power supply devices (more particularly,a pulse generator or brushless power driver), depending on theconditions of use of the device. Advantageously, coils 20, 22 can bemade of a thin sheet wound on the respective arm, to reduce hysteresislosses, Foucault currents on the horizontally exposed surface and skineffect. Of course, opposite coils are connected with oppositepolarities.

Like magnets 14, arms 17 a, b, 19 a, b of yokes 16, 18 may have acircular cross section or a different curvilinear cross-section or yet apolygonal cross section, either convex (in particular square orrectangular) or concave. Non-regular shapes of the magnets and/or theyoke arms and/or different cross-sectional shapes for the magnets andthe yokes can also assist in reducing cogging which, as known, is on thecontrary favoured by strongly symmetrical structures. Whatever the crosssectional shapes of the arms and the magnets, it is important that theareas thereof have sizes that are similar or substantially the same. Thesimilarity or substantial equality of the sizes of the areas of themagnets and the arms is necessary to ensure uniformity of the fluxdensity circulating in yokes 16, 18 and magnets 14.

By using magnets and arms with circular cross sections, a sinusoidalbehaviour of the overlap of the facing surfaces of a magnet and an arm(see FIG. 4) is obtained while the rotor is rotating, and this, in caseof use of the device as a generator, will result in an almost puresinusoidal electromotive force (emf). Considerations of commercialavailability of the components and of reduction of the cogging couldhowever lead e.g. to using magnets with circular cross section and yokeshaving arms with square cross section, the side of which issubstantially equal to the magnet diameter. In this case the emfgenerated will still be almost sinusoidal, with some higher orderharmonics that however do not substantially cause losses, taking intoaccount the large bandwidth of the materials utilisable for constructingthe yokes. Note that, taking into account the transverse sizes that canbe assumed for the magnets and the arms (e.g. a few centimetres), therequirement of similarity of the magnet and arm areas is still met.

By considering, for sake of simplicity of description, magnets and armswith the same circular cross section, and denoting by D their diameter,in order to ensure the symmetry of the produced waveform it is necessarythat the arms of each yoke 16, 18 are spaced apart by a distance D, sothat the length of each yoke is 3D. In correspondence of yokes 16, 18,rotor 12 will therefore have a circumference whose length is 4D·N, whereN is the number of yokes in a ring. Thus, it is possible to build rotorsenabling mounting the desired number of yokes or, conversely, the numberof yokes will be imposed by the rotor size. Moreover, for a given rotordiameter, it is also possible to vary the number of yokes by varying thediameter of the circumference defined by the yokes and the magnets(i.e., in practice, by varying the distance of the magnets from the edgeof rotor 12).

Number M of magnets 14 is related with number N of the yokes and dependson the kind of device that is to be built. For a synchronous machine,relation M=2N applies, so that the distance between subsequent magnets14 is equal to their diameter D and, in a static configuration of device10, a pair of subsequent magnets 14 can be located exactly in front ofboth arms of a yoke 16 or 18. On the contrary, in case of anasynchronous machine, relation M≠2N applies, M being an even number, andthe distance between subsequent magnets 14 is smaller or greater than D,depending on whether M>2N or M<2N.

The arms of yokes 16, 18 end with plane surfaces parallel to thesurfaces of rotor 12 and magnets 14. Each pair of yokes 16, 18 forms amagnetic circuit with a facing pair of magnets 14, which circuit isclosed through the air gaps separating the yokes from the magnets. Apair of yokes 16, 18 with the respective coils 20, 22 will also bereferred to hereinafter as “magnetic pliers”.

As better shown in the diagram of FIG. 3, the ends of arms 17 a, b, 19a, b of yokes 16, 18 are slightly spaced apart from the facing poles ofthe respective pair of magnets 14, thereby forming air gaps 24 a, 24 band 26 a, 26 b, respectively, intended to enable on the one side discrotation, by avoiding the contact between magnets and yokes, and on theother side desaturation of the magnetic circuit. Since rotor 12 andstator 16, 18 have plane surfaces, mechanical machining allows obtainingvery small air gaps and hence high efficiency. Note that, for sake ofclarity, the spacing between the yoke arms has been exaggerated in thedrawing.

Turning back to FIG. 1, an external casing 28, made so as to enablepassage and rotation of shaft 13, keeps the rotor and the stator ofdevice 10 assembled. Moreover, the yokes are mounted onto individualsupports, not shown in the drawing and discussed in more detail lateron, enabling an independent adjustment of the positions of yokes 16, 18relative to magnets 14 through a translational movement along threeorthogonal axes x, y, z and a pivotal movement, indicated by arrows Ω1,Ω2, Ω3, about the same orthogonal axes (see FIG. 24).

This allows an easy mounting of the yokes and an optimisation of theirpositions when assembling the device, as well as a maximisation of theefficiency of the device.

The possibility of independent adjustment of the axial positions of theyokes allows not only minimising the widths of air gaps 24, 26 so as tomaximise efficiency, but also changing such air gaps during operation,for adapting the action of the magnetic pliers to the requirements ofthe different operation phases, as it will become apparent from thedescription of some applications of the invention. Moreover, in case ofa device having both generator and motor modules, at the start up, thegenerator function may temporarily be disabled or adjusted to a limitedvalue in order to facilitate starting, whereas the motor modules can bebrought closer in order to increase acceleration. Furthermore, anincrease of the air gap can be exploited as a safety feature in case ofoverheating: such increase in the air gap causes an increase of thecircuit reluctance, so that the concatenated voltage in the coils, andhence the temperature, is reduced. In general, it is possible to excludeone or more yokes that do not operate properly, while the rest of thedevice continues operating.

The possibility of an adjustment in a plane perpendicular to therotation axis also is a safety feature that can be used in alternativeto increasing the air gap in case of overheating: indeed, also the lossof alignment of yokes and magnets causes the increase of the circuitreluctance leading to the reduction of the concatenated voltage andhence of the temperature in the conductors.

Moreover, in case of machines intended to generate an almost constantpower with important variations in the number of revolutions, thecapability of radially and axially adjusting the positions of the yokescan be exploited to adjust the value of the concatenated power.

Advantageously, as it will be discussed later on, the stator supportsinclude rolling devices, such as rollers or balls, arranged to roll onthe outer perimeter of disc 12 to allow keeping air gaps 24, 26 betweenyokes 16, 18 and magnets 14 constant and compensating for axial andradial oscillations of rotor 12 as well as for thermal expansion. Thisis of particular interest in large-size machines, where radial or axialdisplacements, oscillations, resonance and mechanical and thermaldeformations of the rotor can be important.

Each yoke with its coils, its supports and the means controlling thesupport displacements, including any necessary position and temperaturesensor, can be considered as an elementary stator cell that isreplicated to form the whole device, which thus has a modular structure.Thus several different arrangements can be easily obtained, as it willbecome apparent from the rest of the description.

The material of magnetic yokes 16, 18 can depend on the applications ofthe device.

For high frequency applications, the preferred materials are highpermeability, low residual flux and low magnetic reluctance ferrites(ferroceramic materials). Use of ferrites is advantageous for thefollowing reasons:

-   -   ferrites allow high flux density (about ½ Tesla);    -   ferrites are materials that can be sintered, and hence they        allow making structures and shapes suitable for maximising        efficiency;    -   ferrites exhibit efficiency curves the maxima of which fall        within a broad frequency range, even up to some Megahertz, and        hence are perfectly compatible with the frequencies of passage        of the magnets in the applications envisaged for the invention;    -   given the high electrical resistivity of the material forming        the ferrites and the low value of residual magnetisation with        narrow hysteresis cycle at high frequencies, very low losses in        the ferroceramic material and very low electromagnetic losses        occur, whereby the efficiency is increased;    -   ferrites enable converting the energy deriving from spurious        harmonics of the waveform, this being especially useful for        applications where great diameters and high numbers of        revolutions are required;    -   ferrites have a low specific weight (about half that of iron),        this being of importance in aeronautical applications;    -   ferrites have a capability of self-protection in the case of        over-heating, because of the low Curie temperature Tc, around        250° C. As known, the magnetic permeability of the ferrites at        temperature exceeding Tc is substantially 0 (see FIG. 25): thus,        if the yoke temperature reaches Tc, the overall reluctance of        the circuit considerably increases and takes a value        substantially corresponding to that of a circuit in air, so that        the concatenated voltage decreases to very low values. This        property can be exploited as an alternative to the yoke        displacement.

At relatively low operating frequencies, from some Hertz to someKilohertz (e.g. up to 3 KHz), the yokes can be made of iron-siliconsheets, e.g. with a thickness of 5 or 10 hundredths of millimetre. Forfrequencies from 1 KHz to some ten KHz (e.g. up to 20 KHz) an Ni—Znferrite, such as N27 produced by EPCOS, can be used instead. Ni—Znmaterials are characterised by high operating temperatures, very highresistivity (of the order of 100 kΩ/m) and limited hysteresis losses.Also Mn—Zn ferrites, such as the Ferroxcube materials mentioned above,e.g. MnZn 3C90-6, or Mn—Ni materials can be suitable.

The device according to the invention can act as a wireless generatorand a brushless motor.

In order to disclose the operation principle of device 10 as agenerator, it is suitable to recall the operation principle of atransformer. In a transformer, a dynamic variation of the voltage acrossthe electric circuit of the primary winding causes a flux variation inthe coil through which current flows, which variation is induced on thewhole closed magnetic circuit. The flux variation in the closed magneticcircuit originates a secondary efm, proportional to the number ofconcatenated turns, in the secondary winding.

In the case of the invention, the flux variation occurs by making disc12 with magnets 14 rotate between magnetic yokes 16, 18. In such case, apair of facing magnetic yokes 16, 18 receive the flux variation due tothe alternate passage of permanent magnets 14 with opposite polaritiesbetween the same yokes, thereby inducing, across coils 20, 22, efm'soriginating voltages V1 to V4 (FIG. 3). In other words, by applying arotary torque to disc 12, an efm is induced in each coil 20 a, 20 b and22 a, 22 b, respectively, concatenating the flux variations due to thealternation of the polarities of permanent magnets 14. By looking at therelative positions of magnets 14 and of the facing surfaces of the yokesin a ring, e.g. yokes 16, shown in FIG. 4, it can be seen that duringrotation of rotor 12 the facing areas progressively overlap resulting ina substantially sinusoidal increase of the flux and hence of the inducedvoltage.

Voltage −ΔΦ/Δt generated, where ΔΦ is the magnetic flux variation and Δtis the time elapsing between the passage of two magnets in front of ayoke arm, depends on the size of rotor 12, number M of the magnets(hence, number N of dipoles) and the peripheral rotor speed. With largerotor discs, allowing a high M, a high frequency of magnet passage, andhence a high voltage, can be obtained even with relatively low rotationspeeds.

More particularly, in case of a synchronous machine, each coil 20, 22generates a waveform in phase with the waveforms of the other coils andforms an independent generator. As known, depending on whether the coilsare connected in series or in parallel, a voltage 2N times that of asingle coil but with the same current or, after rectification, a currentequal to the current sum but with the same voltage, respectively, can beobtained. In this second case, a suitable filter can be required.

In case of an asynchronous machine, each coil generates an efm that isphase shifted by ±2π/2N relative to the adjacent coil and, in one periodof rotation of disc 12, after rectifying the waveform, 4N half waveswill be obtained with a ripple factor that is 4N times smaller than thatof a single-phase waveform, so that no filtering and smoothingoperations are required. Note that, in the asynchronous machine, thenumber of magnets and yokes will advantageously be such as to produce asinusoidal waveform or the like (i.e., the combination M=N will beavoided).

In order to evaluate the performance of the device, reference is made tothe following example concerning an aeronautical application. It isassumed that the ring of magnets 14 has a radius of about 1 m and themagnet pitch is about 10 cm (hence D is about 5 cm). Being thecircumference somewhat longer than 6 m, the ring can comprise aboutsixty magnets 14. If the device is mounted on a compressor stage in aturbine, the rotation speed is generally about 12,000 rpm, i.e. 200 rps.Consequently, the frequency of magnet passage is about 12,000 Hz and Δtis about 80 μs. Since the shorter transition time Δt, the higher theinduced voltage, energy characterised by high voltage with highfrequency and low current will be produced. This feature affords furtheradvantages, since high voltages and high frequencies enable using copperwires with reduced cross-sectional size for coils 20, 22 and, moreover,ferromagnetic materials for energy handling and conditioning become verysmall: this results in a weight reduction, which is particularlyimportant for many applications, as it will become apparent hereinafter.

Device 10 can be used in reversible manner as a brushless motor byapplying a voltage variation with phase rotation. The resulting polarityinversion induces a force onto permanent magnets 14, which consequentlymake disc 12 rotate. In such case, the voltage applied to the coilscreates a pair of fluxes with opposite polarities, making the disc moveto allow magnets 14 to be positioned opposite yokes 16, 18 in lined-upmanner and with opposite polarities. In case of a synchronous motor, aprogressive phase increase is to be caused on all coils to start themotion. In case of an asynchronous motor, the control is simplifiedthanks to the phase shift between the rotor and the stator resultingfrom the construction, and it will be sufficient to unbalance any of thecoils to make the machine rotate.

Like in conventional brushless motors, the positions of magnets 14relative to stator 16, 18 are detected. Thus, as soon as the systemreaches a stability condition, the control circuitry starts a phaserotation which causes the rotor to displace again to search a newstability point. By progressively increasing the frequency of suchcontrol pulses, a rotor acceleration is caused.

The main features, in case of operation as a motor, are:

-   -   high acceleration torque: indeed, the force is applied to the        periphery of disc 12, which can have a great radius (torque        arm); as said, a great radius allows mounting a great number of        magnetic dipoles cooperating in operating the motor, and hence        results in a high overall force;    -   high number of revolutions, depending on the excitation        frequency of the device (see for instance the considerations        about the performance made in connection with the operation as        generator).

Moreover, as said for the generator, since the rotor and the stator aretwo parallel surfaces, the mechanical machining allows obtaining verysmall air gaps and consequently high efficiency.

Note that, thanks to the modular structure of the device and to theindependence of the various magnetic circuits, the generator and motorfunctions can be simultaneously present in a same device, in particularalternate cells can act as a generator or as a motor. The generatorcells can thus be used as position detectors to provide the feedback forthe motor function. Actually, a generator cell supplies a voltage thatis proportional to the position of the magnets passing in front of itand, being the relative position of the generator and motor cells known,the rotor position relative to the generator and a motor cell can beimmediately obtained. This allow adjusting the pulse for the motor cellso that it has the precise phase required to obtain the motion in abrushless machine.

In the alternative, the position feedback could be provided also by Halleffect detectors or by an ancillary winding: however, taking intoaccount that Hall effect detectors do not properly operate attemperatures exceeding 150° C., the latter solution could be preferable.

FIGS. 5 and 6 are representations similar to FIGS. 2 and 3, relating toa variant embodiment in which rotor 12 is made of a ferromagneticmaterial. Identical elements in both pairs of Figures are denoted by thesame reference numerals. In this case, the stator comprises a singlering of yokes 16, with respective coils 20 a, 20 b, located oppositemagnets 14 that, in turn, are glued to the surface of rotor 12 facingyokes 16 (see FIG. 6). A suitable material for gluing magnets 14 torotor 12 is for instance loctite hisol 9466. Moreover, in order to makegluing easier, rotor 12 can be equipped with a guide of aluminium orresin (not shown), capable of defining the positions of magnets 14 andhaving containment, strengthening and desaturation functions. Shouldgluing be not sufficient to withstand the effects of centrifugal forcesat high rotation speeds, other measures of keeping the magnets inposition can be taken, as it will be disclosed further on. In thisembodiment, the magnetic circuits are closed between a pair of magnets14 and one yoke 16 through disc 12 and air gaps 24 a, 24 b. Moreparticularly, as shown in FIG. 6, a magnetic circuit comprises: the Npole of a first magnet 14; air gap 24 a; yoke 16 with coils 20 a and 20b; air gap 24 b; the S pole of a second magnet 14; the N pole of thesecond magnet; disc 12; the S pole of the first magnet. The operationprinciple of this variant embodiment is the same as that of theembodiment shown in FIGS. 1 to 3, the difference being only related withthe different number of coils.

By connecting the magnets facing a same yoke by thin ferromagneticsheets for closing the magnetic circuit between the arms of a yoke and apair of magnets, the embodiment with a single yoke ring can also be usedin case of a rotor made of non-ferromagnetic material.

This variant embodiment enhances the lightness characteristics of thedevice.

FIG. 7 shows another variant embodiment in which yokes 16, 18 are notdistributed along the whole circumference of disc 12, but only along oneor more discrete arcs thereof, two in the illustrated example. Thepossibility of having reduced yoke sets is one of the advantagesafforded by the modular structure of the invention. Each set can eveninclude a single yoke. This variant embodiment is suitable forapplications in which the powers (for both the generator and the motorfunctions) obtained by a set of elementary cells extending the wholecircumference would be excessive. Of course, even if this variant hasbeen shown for a device of the kind shown in FIGS. 1 to 3, with a yokeset on each side of rotor 12, it is applicable also to the case of asingle yoke set shown in FIGS. 5 and 6.

FIGS. 8 to 12 relate to an embodiment of the invention with a radialarrangement of the magnets and the yokes. Elements already discussedwith reference to the previous Figures are denoted by the same referencenumerals, with the addition of a prime.

In the radial embodiment, rotor 12′ is a cylindrical body bearingmagnets 14′ with alternate orientations on its side surface. Like in theaxial embodiment, two sets of yokes 16′, 18′ (FIG. 8) or only one set16′ or 18′ (FIGS. 9 and 10) can be provided, depending on the materialof rotor 12′. The yokes have radially directed arms on which coils 20′,22′ are wound. In the solution with a single yoke set, the yokes may belocated either externally or internally of rotor 12′, as shown in FIGS.9 and 10, respectively. The arrangements shown in FIGS. 9 and 10 will bereferred to as “internal rotor” and “external rotor” arrangements,respectively. In the radial embodiment, facing surfaces of the rotor andthe yoke arms will have the same curvature at any point, to ensure theconstancy of the air gap.

In the external rotor arrangement and in the arrangement with a doubleset of yokes, rotor 12′ is formed on the surface of a large hollowcylindrical chamber within which the or one set of yokes is mounted. Inthe internal rotor arrangement, rotor 12 will still be a ring or disccarried by a shaft 13′. Also in the radial embodiment, yokes 16′ and/or18′ can be distributed in front the whole ring of magnets or in front ofone or more arcs only of such ring.

In the variant shown in FIGS. 11 and 12, the side surface of rotor 12′can bear two adjacent and parallel row of magnets 14′a, 14′b (twinmagnet arrangement), a magnet in one row having opposite orientationwith respect to the adjacent magnet in other row. The arms of a yoke 16′and/or 18′ face one magnet 14′a, 14′b in each ring. As shown in FIG. 12,yokes 16′ (only one is shown) can be arranged obliquely with respect tothe generatrices of the rotor ring and the two magnet rows are thenshifted relative to each other so that also a magnet pair 14′a, 14′bfacing a same yoke is obliquely arranged with respect to thegeneratrices of the rotor ring. This feature also contributes to reducecogging.

It is to be appreciated that, in the twin magnet arrangement, the magnetpairs are always in the same radial plane passing through both yokearms, in both the synchronous and the asynchronous configuration, andthe rotation planes are always common to both the magnets and the yokes.In such case, the magnetic flow either is present on the yoke arms sincethe magnets are in front of the yokes, or no flow circulation takesplace since no magnet is in front of a yoke. This affords the importantadvantage that spurious Foucault losses (i.e. a flow is still present inone arm of a yoke and gives rise to a dispersion towards the rotorthrough the other arm) are eliminated, since there is no phase shiftbetween the arms. In all other arrangements, on the contrary, there isalways a little phase shift between a plane passing through thetransversal axis of the magnet and the planes radially crossing the yokearms, since the arms lie in planes mutually phase shifted by a certainangle: thus, a certain spurious Foucault loss is always present.

All considerations about the yoke adjustability made hereinbefore inrespect of the axial arrangements apply also to the radial arrangements,taking into account that the air gap is now a radial gap instead ofaxial one. For instance, in order to adjust the concatenated power, aradial displacement of the yokes allows varying the air gap andlongitudinal displacement of the yokes relative to the rotation axisallows varying the areas over which magnets and arms overlap.

Note that, even if the twin magnet row and the oblique arrangement ofthe yokes relative to the magnets have been shown only for one of theradial arrangements, they could be adopted also for the other radialarrangements disclosed here as well as for the different variants of theaxial arrangement.

In the embodiments described up to now, it has been assumed that thecoils of a yoke are independent from one another and from the coils ofthe other yokes, and are individually connected to the power driver orthe utilising device. A high number of cells would entail a high numberof connections to the outside, namely at least two connections for eachcoil, and this can be a drawback in terms of complexity of the device.The modular structure of the device can be exploited to reduce thenumber of outside connections, while still having independent coils oneach arm. Looking at the geometrical aspect of the device, in a machinewith N yokes (and hence P=2N arms or polar expansions) and M magnets, itcan be generally observed that a given geometrical phase between thepoles and the confronting magnets occur with a periodicity of X polarexpansions, with:X=P/gcd(P, M)where the abbreviation “gcd” stands for greatest common divisor. Eachcoil in a group of X coils generate efm's phase shifted with respect tothe other coils in the group, and the electrical phases of the coils areidentically repeated in all groups. Coils with the same phase may beconnected together in parallel or in series or with a star, triangle . .. configuration inside the machine, and their common points will beconnected to the outside. Thus, the number of outside connections isreduced to the number of different phases. A modular multiphase machineis thus obtained, where each module includes X polar expansions andY=M/gcd(P, M) magnets. It is also possible to connect to the outside thecoils of alternate modules with inverted phases, so that an X-phase or a2X-phase machine can be obtained with a given pair of values M, P. Ofcourse, when the modular multiphase arrangement is applied to the twinmagnet embodiment, the advantage of the synchronous flow in both arms ofa cell is still maintained. By connecting in parallel or in seriesmodules with the same phase it is possible to increase or reduce at willthe voltage, whereby the same result afforded by the yoke displacementis achieved.

FIGS. 13 to 15 show some exemplary arrangements with different pairs ofvalues P, M, where M is an even number lower than P−2. The Figures referto the radial embodiment, but of course the same considerations apply tothe axial embodiment.

In FIG. 13, P=64 and M=48, so that X=4. This allows obtaining machineswith either four or eight phases, depending on whether the coils inevery second group of four coils have the same phases or inverted phaseswith respect to the corresponding coils in the adjacent group of fourcoils.

In FIG. 14, P=48 and M=40, so that X=6. This allows obtaining machineswith either six or twelve phases, depending on whether the coils inevery second group of six coils have the same phases or inverted phaseswith respect to the corresponding coils in the adjacent group of sixcoils.

In FIG. 15, P=48 and M=32, so that X=3. Three-phase or six-phasemachines can be obtained, depending on whether the coils in every secondgroup of three coils have the same phases or inverted phases withrespect to the corresponding coils in the adjacent group of three coils.

Other asynchronous configurations could be achieved with M even andgreater than P.

This simplification of the external connections can be applied also inthe case of the synchronous machine, where M=P, so that P coils with thesame phase, or P/2 coils with one phase and P/2 coils with the invertedphase can be obtained, and one or two connections only to the outside isor are necessary.

FIGS. 13 to 15 also show a shape of the polar expansions, denoted hereby reference numeral 7, which is particularly advantageous formultiphase machines. Reference is made also to the enlarged views ofFIGS. 16( a) and 16(b). Polar expansion 7 has an enlarged head 7 afacing the magnets, an intermediate stem 7 b with reducedcross-sectional size onto which the coil (denoted here by referencenumeral 21) is wound and a base or foot 7 c for securing polar expansion7 to a support (e.g. the connecting member previously disclosed). Thisshape has the advantage that the active ferromagnetic section of themachine is enlarged while reducing the exposure of the coils to therotating magnets. Stem 7 b is substantially shaped as a rectangularparallelepiped, having the largest surfaces perpendicular to thedirection of rotation of the rotor. Also foot 7 c of the polarexpansions can have larger size than stem 7 b. Polar expansions 7 couldbe individually fastened to a stator support by fastening means 7 d andas shown in FIG. 16( b), a yoke, denoted here by reference numeral 6,will comprise two adjacent expansions 7 joined in correspondence oftheir feet 7 c. The individual mounting is advantageous in that it makeswinding of the coils easier. Moreover, the side surfaces of feet 7 c areslightly inclined, e.g. by a few degrees, so that a certain angle, opentowards the rotor, exists between the axes of stems 7 b in the yoke. Theinclination of the axes of stems 7 b in a yoke 6 provides space forwinding coils of relatively great size.

A further solution for the reduction of the number of externalconnections when using the device as a generator could be rectifying thewaveforms of all coils within the machine, and connecting in parallelthe positive poles as well as the negative poles within the machine, sothat only two output conductors are required. However, such a solutioncould make use of the machine as a motor impossible or extremelydifficult, since all coils are connected together. However, the phasemodularity disclosed with reference to FIGS. 13 to 15 could be exploitedso as to leave some of the cells not connected to the rectifierstructure and to use such cells for the motor function. For instance,considering a machine with 48 polar expansions, the following sequencecould be envisaged: three polar expansions connected through therectifiers and one polar expansion independent and reversible, wherebythirty-six polar expansions are directly rectified and connectedtogether, and twelve independent polar expansions are distributed alongthe circumference with pitch X=4.

FIGS. 17( a) to 17(d) show a magnet embodiment suitable for withstandingthe centrifugal force especially at high rotation speeds, such as thoseencountered when the magnets are mounted on the impeller of a turbine.The magnet is a quadrangular plate 140 whose bases form the N and Spoles of the magnet and whose side surface has a double tapering: moreparticularly, two opposite sides of the magnet are tapered e.g. from topto the bottom, and the other two sides have the inverse tapering. Inother words, the sections according to two planes perpendicular to oneof the magnet bases, such as the planes passing through lines C-C andD-D in FIG. 17( b), are two inverted trapeziums, as shown in FIGS. 17(c) and (d). Such a shape enables transferring the tangential or radialcompression stresses in order to exploit the high resistance tocompression.

If necessary, in case of magnets adjacent to each other, retainingelements (not shown) having a complementary tapering to the facing sidesof the magnets can be provided between adjacent magnets transversally tothe magnet ring and, in case of the twin magnet arrangement, alsolongitudinally between the magnets in the two rows.

Note that, in a variant of the embodiment of FIGS. 17( a) to 17(d), onlyone pair of opposite side faces could be inclined, so that the plate issubstantially wedge-shaped. Also, the same effect of a wedge-shaped ordoubly tapered plate could be obtained by plates shaped as frustums ofcones or pyramids.

As shown in FIG. 18 for an external rotor radial device using yoke 6 ofFIG. 16( b), the resistance to the centrifugal force may be enhanced bythe use of a tangentially operating resilient retaining member 60located between adjacent magnets 140 and arranged to apply a compressionstress on the magnet sides to compensate dimensional variations due totangential stresses. Member 60 can include for instance a leaf springhaving a central portion 60 a fastened to rotor 12′ and two U-shapedside arms 60 b extending from the central portion toward a respectivemagnet 140, so that the legs of the U remote from central portion 60 alean against the magnets. Clearly, either two rows of retaining members60, one for each magnet row, or a single row of member 60 can beprovided. FIG. 18 further shows that adjacent yokes 6 could be separatedby a gap 77 providing a degree of freedom in respect of possiblemechanical interferences due for instance to thermal expansion. The sameeffect could be obtained also by use of retaining members made ofelastomeric material, e.g. Teflon®.

FIG. 19 shows a detail of an embodiment of internal rotor machine usingwedge-shaped magnets 140 with strongly inclined walls. This solution isintended for vey high numbers of revolutions. Magnets 140 are housed inseats 62 formed in the rotor edge and having, e.g. in a planeperpendicular to the rotation axis of the rotor 12′, a substantiallytrapezoidal cross-section, complementary to the correspondingcross-sectional shape of the magnets and are wrapped in a non-conductivesheet 66. The other two sides of magnets 140 engage with clamps 64transversally retaining the magnets.

Note that FIGS. 18 and 19 refer to the twin magnet arrangement and alsoshow thin ferromagnetic sheets 61 connecting magnets confronting a sameyoke.

FIGS. 20 to 22 show a possible support structure for a yoke 16, enablingthe cell displacement and the automatic compensation of deformations orvariations in the position or attitude of the rotor. FIGS. 20 and 21 aretwo very schematic sectional principle views according to two orthogonalplanes, and FIG. 22 is a perspective view in which, for clarity, some ofthe components shown in the sectional views have been omitted.

Such support structure comprise a number of rolling members 50 (four inthe illustrated example, two for each arm, see FIG. 22), such as balls,rollers, roller or ball bearings etc. Those members are arranged to rollover a suitably processed peripheral area 51 of the rotor surface,acting as a track for the rolling members and serve for keeping constantthe air gap. To this end, rolling members 50 are associated withmechanically, hydraulically or pneumatically operated adjusting units52, e.g. hydraulic or pneumatic cylinders or sliding members, which, ina calibration phase of the device, are set so that, in normal operatingconditions, rolling members 50 are spaced apart from rotor 12 and arebrought in contact with rotor 12 only when the latter is displaced fromits proper operating position or becomes deformed. Setting of rollingmembers 50 is such that they are somewhat projecting with respect to thearms, so as to leave a desired air gap when they are rolling over therotor. Rolling members 50 and their adjusting units 52, together withyoke 16 they are associated to, are brought by a bearing structure 54,which is associated with compression springs 56, or other elementshaving the same functions, that are calibrated to contrast anydisplacement of the rotor leading to a variation of said desired airgap.

For giving solidity to the structure, the whole cell consisting of ayoke 16, 18 with its coils 20, 22, its supporting structure 54, themeans causing the position adjustment and generally the yokedisplacements described above and the detectors causing suchdisplacements can be embodied in a resin layer, as shown at 70 in FIG.23, possibly enclosed in a casing, not shown in the Figure. The resincan possibly be charged with powders of materials increasing electricaland/or thermal conductivity, such as boron, silicon carbide, aluminiumor the like.

FIG. 27 shows a principle implementation of a cell and its means for theaxial adjustment. The yoke, e.g. yoke 16, is equipped on its arms 17with two power coils 20 and two signal coils 200, which are surroundedby cooling coils 80. The cell is further equipped with temperature andposition detectors 86, 88 with the relevant signal processing andcontrol circuits 90. For instance, temperature detectors 88 may comprisea thermo-resistor of the positive or negative thermal control type, or athermocouple. As stated above, position detectors 88 (which term ismeant to include also phase detectors and rotation frequency detectors)can be Hall effect detectors or ancillary coils or yet primary powercoils utilised for detecting phases and amplitudes of the currents andthe voltages in the coils of the various arms. Note that even ifdetectors 86, 88 have been shown outside the yoke for sake of an easierunderstanding, they will in fact be located internally of the cell, e.g.together with processing and control circuits 90 at the location shownfor the latter.

Springs 56 contrasting the rotor displacements are mounted withinactuating pistons or cylinders 82, slidably mounted within cylinders 92.In idle conditions of the device, pistons 82 are completely retractedwithin cylinders 92 by springs 84. In operating conditions, cylinders 92cause extension of pistons 82 so that the latter take their steadyworking position. In case of dynamic adjustment, a suitable lineardriver controlled by the electronic control unit of the device modulatesthe push applied to piston 82 depending on the operating requirements.By differently acting on the two pistons 82, tilting of the cell can beobtained. Of course, any hydraulically, pneumatically or mechanicallyoperated device equivalent to the assembly of pistons 82 and cylinders92 can be used.

Detectors 86, 88, processing and control circuits 90 andpistons/cylinders 82, 92 are connected to a central processor (notshown) which, based on the information received from the detectors andthe model of the machine stored inside it, determines the actions to betaken for both the regular operation of the machine and the safetyprocedures. The displacement commands are sent through suitable powerdrivers and actuators of which pistons/cylinders 82, 92 or otheradjusting units are the members connected to the cell.

Cylinders 82, 92 or equivalent units will be provided for controllingtranslation/rotation of the cell along/about the other axes.

A single rolling member 50 with its adjusting piston 52 has been shown,disassembled form the rest of the cell for sake of clarity of thedrawing. Rolling member 50 is associated with shock-absorbing means,e.g. a spring 58, for compensating the impact of the rolling memberitself against the rotor.

The described characteristics of lightness and high efficiency and, incase of use as a motor, of high torque, and the high performance, allowseveral applications for the device, such as for instance:

-   -   turbine-mounted aeronautical generator;    -   starting motor for a turbine;    -   feedback motor for turbine architecture;    -   motor for ship and aircraft propellers;    -   aeronautical propeller for vertical take-off;    -   motor for pumps for gas pipelines and the like;    -   Aeolian generator;    -   industrial generator in general;    -   torque regulator;    -   flywheel for automotive systems;    -   electromagnetic brake with energy recovery;    -   active brake.

Hereinafter, such applications will be shortly discussed.

Aeronautical Generator

This application arises from the need to generate electrical energy onboard aircrafts. Device 10 can be directly mounted on the stages at lowoperating temperature (in such case, blades 15 shown in FIG. 2 will bethe blades of the turbine stage) and allows replacing the conventionalalternators receiving mechanical energy through a speed reduction gearconnected to the turbine axis. The generator of the invention istherefore a solution in line with the modern technologies of electricalenergy conversion by means of switched power supplies, which enableremote driving of actuators, devices and transducers through acompletely electric distribution. Device 10, which is capable ofgenerating electrical energy at high voltage and frequency, withoutdirect contact with the turbine, enables eliminating many of thedrawbacks of the conventional technique. In particular, it islightweight and highly reliable, has a long life, has an easilyexpandable modular construction and requires minimum maintenance.Moreover, it is relatively cheap, in particular with respect to the costof the motor and the gear box.

Starting Motor for Aeronautical Applications and for Turbines in General

The device according to the invention, being wholly reversible, allowsproviding also the starting system for the engines on an aircraft,without additional weight and costs, apart from those of the electroniccontrol units for the brushless motor. On the contrary, the startingsystem often is not provided on aircrafts since it is heavy andexpensive, so that the ignition phase is limited to the aircraft parkingphases only, when an external motor can be used. This choice clearlylimits the flexibility and safety of the aircraft itself. The samecharacteristics of lightness and limited cost also allow employing theinvention as starting motor for turbines in general, also outside theaeronautical field.

Feedback Motor in Turbine Architectures

The low-pressure or high-pressure compressor is brought to a rotationspeed that is no longer linked with the rotation speed of the turbineshaft, but is determined by the electric motor built around andexternally of the compressor (overspeed). This enables optimising thenumber of revolutions and the pressures in the compressors independentlyof the turbine stages, and results in more adjustment possibilities forand in an optimisation of the performance and the consumption.

Motor for Ship Propellers

Electrical ship propulsion can make use of machines of the kindconcerned by the invention since such machines have low noise, can bemounted externally to the hull and, being rigidly connected to thescrew, they can be angularly displaced relative to the longitudinal hullaxis, thereby providing for a high manoeuvrability of the ship. Use ofthe invention in such applications is shown in FIG. 26, where thetwin-magnet radial embodiment of a device 10 according to the inventionis shown integrated onto the periphery of screw 11 of a ship. Thehousing frame has been removed to show the arrangement of device 10. Insuch applications, the invention affords the following advantages:

-   -   high torque in case of great radii and high number of poles        thanks to the arrangement of the motor cells on the screw        periphery;    -   possibility of individual maintenance and adjustment of the        cells;    -   high reliability, since, even in case of failure of one cell,        the other cells can continue operating independently of the        failed one;    -   possibility of operating in harsh and hostile environments,        thanks to the sealing of the cells with the resin;    -   high immunity to screw oscillations relative to the frame thanks        to the peripheral rolling members the cells are equipped with,        since the cells can pivot relative to the screw while keeping        the gap constant.        Motor for Aircraft Propellers and Aeronautical Propeller for        Vertical Take-Off

The advantages of high torque and high reliability make the use of theinvention suitable also in aircraft propellers. The structure of anaircraft propeller using the invention is as shown in FIG. 26. In suchapplications, the device of the invention can work together withgenerator units associated with thermodynamic machines, withaccumulators, fuel-cells, photovoltaic cells etc.

Moreover, since the screw and the ring of magnets/yokes can be orientedalso in horizontal position, e.g. parallel to the wing surface, thepossibility exists of generating a vertical flow for the verticaltake-off; then, after the take-off, the assembly of the screw and thering can be rotated to progressively pass to the horizontal flight. Useof the invention in such an application solves the problems related withthe very high temperatures of the gas flows of the conventionalturbines, which flows, in the vertical arrangement of the turbine, coulddamage the aircraft and the runways.

Motor for Pumps for Gas Pipelines and the Like

The application in this field is based on the same principles as that inship propellers. In this case however the magnets are located inside thepipeline while the yokes are located on an external ring. In this mannerthe absence of any contact and the complete electrical insulationbetween the yokes and the propeller inside the pipeline are ensured. Ahigh reliability and an intrinsic safety are thus achieved, which areparticularly suitable for pumping gases and hydrocarbons.

Aeolian Generator

For such application, blades 15 in the central part of disc 12 will formthe vanes of the Aeolian generator. This application is possible in thatno problem exists in building large discs, capable of housing vanes withthe sizes typical for such application, while keeping however a reducedweight. Thanks to the great number of dipoles that can be mounted onlarge disc and to the low losses of the magnetic circuit, a goodefficiency can be achieved in any wind condition. The plurality ofdipoles allows sizing the structure so as to optimise the trade-offbetween cost and performance.

Industrial Generator

The invention is suitable for use as a generator whenever a rotatingshaft exists, since securing rotor 12 to the rotating shaft (which thusforms shaft 13 of the device) is easy, whereas the ring of magneticpliers 16, 18 can be independently housed since it lacks any mechanicalconnection with the rotating member. The invention is particularlysuitable for use in conjunction with turbines for energy production,since the elements forming device 10 can be easily integrated with theturbine itself.

D.c. Torque Regulator

This application demands that also the whole of yokes 16, 18 isrotatably mounted. If a constant polarity voltage is applied to device10, magnets 14 are stably positioned in a balance condition in front ofmagnetic yokes 16, 18. Thus, by rotating the external portion bearingyokes 16, 18, a similar rotation is induced in rotor module 12 bearingmagnets 14. This joint rotation of the stator and the rotor continuesuntil attaining the maximum torque, which is given by the product of thetangential force jointly applied to the disc and the yokes by the arm(radius of the magnet ring), whereafter a constant torque slidingstarts. In this case, if multiple revolutions at constant torque arerequired, it is necessary to provide a rotary collector to allow currentflow during rotation.

By varying the voltage level, the concatenated force is varied untilsaturating the ferromagnetic circuit.

A.c. Torque Regulator

In this case the device according to the invention acts as described inconnection with the motor: yet, at the end of a screwing stroke, thedevice stops and the applied torque is reset, like in the case of thed.c. torque regulator. In this case however rotary collectors are notrequired to allow current flow.

D.c. or a.c. torque regulators using the invention can be used forinstance in machines for bottle cap screwing, which must operate withconstant torque even when the thread is completely screwed. Suchrequirement is particularly severe in foodstuff field and inchemical-pharmaceutical industry.

Electromagnetic Flywheel

An important application of the invention is for recovering energyduring deceleration, by converting mechanical energy into electricalenergy, storing electrical energy into mixed accumulator systems (i.e.,systems including devices operating in different times and havingdifferent accumulation and supply characteristics) and returning it,thanks to the device reversibility, as mechanical energy during theacceleration phase. The device substantially acts as an electromagneticflywheel.

The structure of a system using the device according to the invention asan electromagnetic flywheel is schematically shown in FIG. 28.

In the structure, the electromagnetic flywheel, i.e. device 10, ismounted on the drive shaft between engine 30 and the load, upstream ofgear box 32. Under such a condition, flywheel 10 is directly rotated atthe same speed as the drive shaft (generally, approximately from 1,000up to and beyond 20,000 rpm). Flywheel 10 can be arranged transversallyof the motor axle, centrally on the car, thereby minimising gyroscopiceffects, which however are low since the moving member (rotor) has a lowmomentum of inertia.

Flywheel 10 is connected on the one side to the units that, in thewhole, form energy recovery assembly 33, and on the other side to theunits that, in the whole, form energy supply assembly 35. Assemblies 33,35 are connected to the input and the output, respectively, ofaccumulator 40 that, as said, can be a mixed accumulator system. Energyrecovery assembly 33 comprises an inverter 34 that can be connectedbetween flywheel 10 and a current generator 38 by brake control 36.Current generator 38 then supplies accumulator 40. Energy supplyassembly 35 in turn comprises a phase regulator 42, connected toaccumulator 40 and controlled by a flywheel position encoder 44, andbrushless motor slaving units 46, that can be connected to flywheel 10by accelerator control 48.

In idle condition (i.e. when brake control 36 is not operated), coils20, 22 (FIGS. 1 to 3) are kept in open circuit condition and are movedaway from rotor 12, thereby increasing the air gap in order to annulbraking effects during normal run, so that the counter-electromotivefeedback force is substantially 0. During braking or recovery phase, theelectric circuit of the coils is closed on inverter 34 thereby makingcurrent flow and generating a counter-electromotive force on disc 12 offlywheel 10. Moreover, both rings of yokes 16, 18 are moved closer todisc 12 so that the device operates with the minimum air gap and hencethe maximum counter-electromotive force. That force causes a reductionin the kinetic energy, thereby braking the vehicle and simultaneouslygenerating high-frequency electric energy that is transformed by currentgenerator 38 so that it can be stored in accumulator 40.

During acceleration, the reverse supply process is actuated. In thisphase, the flywheel acts as a brushless motor. When accelerator control48 is actuated, a voltage variation with phase rotation is applied andthe polarity inversion then induces a force on permanent magnets 14 thatmake disc 12 rotate. For the rest of the operation, the considerationsalready made in respect of the operation as a motor apply. The presenttechnologies also allow supplying high energy amounts in short time:this enables attaining, during the supply phase, very high accelerationtorques and very steep curves for the motor response.

Electromagnetic Brake

A device 10 according to the invention, mounted between a thermodynamicengine 20 and transmission units 32 of a vehicle as shown in FIG. 28,may also act as an electromagnetic brake. In such an application, duringnormal operation, coils 20, 22 (FIGS. 1 to 3) are kept in open circuitcondition and yokes 16, 18 are kept at a great distance from the rotoras in the above case, so that the counter-electromotive feedback forceis substantially 0. When braking, the yokes are moved closer to therotor as before, and the electric circuit of the coils is closed on aresistive load (instead of being closed on an inverter, as in theflywheel case), and the braking energy is transformed in thermal energywhile a counter-electromotive braking force acts on the disc.

Active Brake

Another possible use of the invention is as an active brake. Theprinciple is a development of that described for the flywheel, save thatin the present case energy accumulation takes place also during thenormal operation or run phase of the vehicle. During the braking phase,the circuit of coils 20, 22 not only is closed on a load, but is alsodriven so as to operate as a counter-rotating motor: energy then flowsfrom accumulator 40 (FIG. 28) to the braking device, thereby reducingbraking time. By arranging a device 10 on the axle of each wheel, wheellock can also be avoided: when braking, the active braking action can beindependently distributed to each wheel, thanks to the possibility ofaxially adjusting the relative position of the rotor and the stator, anda counter-rotating action can be provided in differentiated manner,suitable for compensating the unbalanced loads typical of an emergencybraking. The general advantages of such an application are related withthe high torque of the device, the intervention rapidity and the lowpower consumption, since the energy concerned is high but for shortperiods.

It is clear that the above description has been given only by way of nonlimiting example and that changes and modifications to the describedembodiment, especially in respect of shapes, sizes, materials, kinds ofcomponents and so on, are possible without departing from the scope ofthe invention. For instance, also when the yokes, and hence the cells,form a complete ring in front of the rotor, they do not need to beregularly distributed along the rotor circumference. This non-regulardistribution is useful in reducing cogging, as well as when the devicecomprises both generator and motor modules or has a multiphasestructure. If necessary, the non-regular distribution of the statorcells can be electronically compensated for by the control system of thedevice. Also, further applications besides those mentioned above arepossible.

The invention claimed is:
 1. An electromagnetic device with reversiblegenerator-motor operation, the device comprising: a rotor rotating aboutan axis and bearing a plurality of magnets distributed at regularintervals there around and with alternate orientations in asubstantially ring-shaped pattern; a stator comprising at least one setof individual magnetic yokes each having a pair of projecting arms thatextend towards the magnets and bear a respective coil for electricalconnection to a utilising device or a power driver, a magnetic yoke ineach set being part together with a pair of magnets confronting the yokearms at a given instant, and an air gap separating the yoke from themagnets, of a same closed magnetic circuit; the individual magneticyokes being independently mounted on supports that are adjustable by amechanism under the control of an electronic control unit to dynamicallyadjust the positions of the individual magnetic yokes relative to themagnets during operation of the device.
 2. The device as claimed inclaim 1, wherein said supports are axially adjustable through atranslational movement.
 3. The device as claimed in claim 1, whereinsaid supports are further adjustable through a pivotal movement about atleast one axis.
 4. The device as claimed in claim 3, wherein saidsupports are adjustable through a pivotal movement about three axes. 5.The device as claimed in claim 1, wherein said stator includes a singleset of individual magnetic yokes.
 6. The device as claimed in claim 5,wherein said rotor is made of ferromagnetic material, and said magneticcircuit comprises a pair of magnets and one yoke facing the magnet pairand it is closed through the rotor and the air gap separates the yokefrom the magnets.
 7. The device as claimed in claim 5, wherein saidrotor (12; 12′), in areas not occupied by the magnets (14; 14′; 14′a,14′b; 140), is made of non-ferromagnetic material, the magnets (14; 14′;14′a, 14′b; 140) facing a same yoke are connected by ferromagneticelements (61), and said magnetic circuit comprises a pair of magnets(14; 14′; 14′a, 14′b; 140) and one yoke (16; 16′) facing the magnetpair, and it is closed through the ferromagnetic elements (61) and anair gap separating the yoke from the magnets.
 8. The device as claimedin claim 2, wherein said magnets are glued onto the surface of the rotorfacing the yokes.
 9. The device as claimed in claim 1, wherein: saidrotor (12, 12′), in areas not occupied by the magnets (14; 14′; 14′a,14′b; 140), is made of non-ferromagnetic material; said stator (16, 20a, 20 b, 18, 22 a, 22 b; 16′, 18′, 20′, 22′) includes a first and asecond set of magnetic yokes (16, 18; 16′, 18′; 6) symmetricallyarranged relative to the rotor (12, 12′), and said magnetic circuitcomprises a pair of adjacent magnets (14; 14′; 14 a, 14 b; 140) and onemagnetic yoke (16, 18; 16′, 18′; 6) in each of the first and the secondset.
 10. The device as claimed in claim 1, wherein said magnets aremagnetised areas in the rotor and they form a succession of alternatelyopposite poles onto the rotor surfaces facing the individual magneticyokes.
 11. The device as claimed in claim 1, wherein said individualmagnetic yokes are arranged in front of one arc or of a number ofdiscrete arcs of magnets in the magnet ring.
 12. The device as claimedin claim 1, wherein said individual magnetic yokes are distributed infront of the whole magnet ring.
 13. The device as claimed in claim 12,wherein said rotor bears a number M of magnets chosen out of: 2N, Nbeing the number of the magnetic yokes in the or each set; an evennumber different from 2N.
 14. The device as claimed in claim 1, whereinthe coil of each yoke arm is individually connected to a utilisingdevice or a power driver.
 15. The device as claimed in claim 13, whereinthe coils of the yoke arms having a same geometrical phase relationshipwith a confronting magnet are connected together inside the device andhave a common connection to a utilising device or a power driver. 16.The device as claimed in claim 13, wherein the coils of alternate yokearms having a same geometrical phase relationship with a confrontingmagnet are connected together inside the device and have respectivecommon connections with opposite phases to a utilising device or a powerdriver.
 17. The device as claimed in claim 14, wherein the coils of atleast some yoke arms are connected to a utilising device, and the coilsof at least some other arms are connected to a power driver.
 18. Thedevice as claimed in claim 1, wherein said individual magnetic yokesbear a first coil for electrical connection to a utilising device or apower driver, and a second coil acting as a feedback detector.
 19. Thedevice as claimed in claim 1, wherein said rotor (12′) is a cylindricalbody bearing the plurality of magnets (14′a, 14′b) on its side surfaceand the plurality of magnets are arranged in two parallel rows (14′a,14′b) on said side surface, a magnet in one row having oppositeorientation to an adjacent magnet in the other row and each yoke (16′)being arranged so as to bridge both rows of magnets (14′a, 14′b). 20.The device as claimed in claim 19, wherein each yoke (16′) and therespective pair of magnets (14′a, 14′b) bridged by it are obliquelyarranged with respect to the generatrices of the rotor (12′).
 21. Thedevice as claimed in claim 1, wherein said arms (17 a, 17 b, 19 a, 19 b;7) and said magnets (14; 14′; 14′a, 14′b; 140) have a cross sectionalshape chosen out of the group including: circular cross section;non-circular curvilinear cross section; concave polygonal cross section;convex polygonal cross section, in particular square or rectangular; andwherein facing areas of the magnets (14; 14′; 14′a, 14′b; 140) and thearms (17 a, 17 b, 19 a, 19 b; 7) have similar sizes.
 22. The device asclaimed in claim 21, wherein said yoke arms and said magnets havedifferent cross-sectional shapes.
 23. The device as claimed in claim 1,wherein said magnets are magnetic bodies (140) having a shape chosen outof: wedge shape; a polyhedral shape with quadrangular bases connected byinclined side faces, the inclinations of the two pairs of opposite sidefaces being such that they produce an opposite tapering of the plate;frusto-conical shape.
 24. The device as claimed in claim 23, whereinadjacent magnets (140) have located therebetween tapered retainingmembers having a complementary tapering to that defined by confrontingsurfaces of said adjacent magnets (140).
 25. The device as claimed inclaim 23, wherein adjacent magnets (140) have located therebetweentangentially operating resilient or elastomeric retaining members (60).26. The device as claimed in claim 1, wherein each yoke arm (7) includesa base (7 c) for being secured to a support, a stem (7 b) extending fromthe base (7 c) towards the magnets (14′; 140) and having the coil (21)wound thereon, and a head (7 a) joined to the stem end opposite to thebase (7 c), and wherein said head has a greater cross sectional sizethan the overall cross sectional size of the stem (7 b) and the coil(21) and is arranged to hide the coil (21) to a confronting magnet (14′;140).
 27. The device as claimed in claim 26, wherein each yoke (6)comprises a pair of individually mounted arms (7) defining an angle opentowards the magnets (14′; 140), and wherein a gap (77) is providedbetween the bases (7 c) of two adjacent arms (7) respectively belongingto two adjacent jokes (6).
 28. The device as claimed in claim 1, whereinsaid yoke arms (17 a, 17 b, 19 a, 19 b) are connected by a member havinga length equal to the transversal size of the arm, and facing sides ofadjacent arms in adjacent yokes (16, 18; 16′, 18′) are spaced apart by adistance equal to the transversal size of the arm.
 29. The device asclaimed in claim 1, wherein said individual magnetic yokes are made of amaterial chosen out of the group: high permeability, low residual fluxand low magnetic reluctance ferrites; iron-silicon sheet; Ni—Zn or Mn—Znferrites; Mn—Ni materials.
 30. The device as claimed in claim 1, whereinthe supports of the individual magnetic yokes are equipped with rollingmembers arranged to cooperate with the rotor surface to keep the airgaps between the individual magnetic yokes and the magnets constant andto compensate for axial and radial oscillations of the rotor.
 31. Thedevice as claimed in claim 1, wherein the individual magnetic yokes areassociated with temperature detectors and position detectors connectedwith processing and control circuitry of said electronic control unitarranged to actuate displacement means on the supports to vary the airgap and/or the degree of overlapping between the magnets and theconfronting arms in order to vary the concatenated voltage in theindividual coils in response to the detected temperature and/orposition.
 32. The device as claimed in claim 30, wherein the individualmagnetic yokes together with their coils, their supports, support andadjusting units for the rolling members, the detectors and the controland processing circuitry are embedded within a resin layer, possiblycharged with powder materials increasing thermal conductivity.
 33. Thedevice as claimed in claim 32, wherein said resin layer is provided withheat dissipating members.
 34. The device as claimed in claim 1, whereinsaid device (10) is integrated in an impeller of an apparatus driven bythe motion of a fluid.
 35. An apparatus having an impeller driven by themotion of a fluid, characterised in that said impeller has integratedtherein a device (10) as claimed in claim
 1. 36. The apparatus asclaimed in claim 35, wherein said apparatus is chosen out of the groupincluding: turbines, in particular for aeronautical or naval engines,screws of propellers for aeronautical or naval applications, pumps forgas pipelines, Aeolian generators.
 37. The device as claimed in claim 1,wherein the electronic control unit includes signal processing andcontrol circuits for receiving signals from position detectors providedwithin the individual magnetic yoke mounting supports to thereby controlthe dynamic adjustment of the position of individual magnetic yokes.